Sensors

219 KiB

Open AccessArticle

Arrays of Regenerated Fiber Bragg Gratings in Non-Hydrogen-Loaded Photosensitive Fibers for High-Temperature Sensor Networks

by Eric Lindner, Christoph Chojetztki, Sven Brueckner, Martin Becker, Manfred Rothhardt, Johan Vlekken and Hartmut Bartelt

Sensors 2009, 9(10), 8377-8381; https://doi.org/10.3390/s91008377 - 22 Oct 2009

Cited by 28 | Viewed by 12713

Abstract

We report about the possibility of using regenerated fiber Bragg gratings generated in photosensitive fibers without applying hydrogen loading for high temperature sensor networks. We use a thermally induced regenerative process which leads to a secondary increase in grating reflectivity. This refractive index [...] Read more.

We report about the possibility of using regenerated fiber Bragg gratings generated in photosensitive fibers without applying hydrogen loading for high temperature sensor networks. We use a thermally induced regenerative process which leads to a secondary increase in grating reflectivity. This refractive index modification has shown to become more stable after the regeneration up to temperatures of 600 °C. With the use of an interferometric writing technique, it is possible also to generate arrays of regenerated fiber Bragg gratings for sensor networks. Full article

(This article belongs to the Section Chemical Sensors)

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820 KiB

Open AccessArticle

Microgyroscope Temperature Effects and Compensation-Control Methods

by Dunzhu Xia, Shuling Chen, Shourong Wang and Hongsheng Li

Sensors 2009, 9(10), 8349-8376; https://doi.org/10.3390/s91008349 - 21 Oct 2009

Cited by 96 | Viewed by 14204

Abstract

In the analysis of the effects of temperature on the performance of microgyroscopes, it is found that the resonant frequency of the microgyroscope decreases linearly as the temperature increases, and the quality factor changes drastically at low temperatures. Moreover, the zero bias changes [...] Read more.

In the analysis of the effects of temperature on the performance of microgyroscopes, it is found that the resonant frequency of the microgyroscope decreases linearly as the temperature increases, and the quality factor changes drastically at low temperatures. Moreover, the zero bias changes greatly with temperature variations. To reduce the temperature effects on the microgyroscope, temperature compensation-control methods are proposed. In the first place, a BP (Back Propagation) neural network and polynomial fitting are utilized for building the temperature model of the microgyroscope. Considering the simplicity and real-time requirements, piecewise polynomial fitting is applied in the temperature compensation system. Then, an integral-separated PID (Proportion Integration Differentiation) control algorithm is adopted in the temperature control system, which can stabilize the temperature inside the microgyrocope in pursuing its optimal performance. Experimental results reveal that the combination of microgyroscope temperature compensation and control methods is both realizable and effective in a miniaturized microgyroscope prototype. Full article

(This article belongs to the Special Issue Modeling, Testing and Reliability Issues in MEMS Engineering - 2009)

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440 KiB

Open AccessArticle

A CMOS-Compatible, Low-Noise ISFET Based on High Efficiency Ion-Modulated Lateral-Bipolar Conduction

by Sheng-Ren Chang and Hsin Chen

Sensors 2009, 9(10), 8336-8348; https://doi.org/10.3390/s91008336 - 21 Oct 2009

Cited by 17 | Viewed by 15384

Abstract

Ion-sensitive, field-effect transistors (ISFET) have been useful biosensors in many applications. However, the signal-to-noise ratio of the ISFET is limited by its intrinsic, low-frequency noise. This paper presents an ISFET capable of utilizing lateral-bipolar conduction to reduce low-frequency noise. With a particular layout [...] Read more.

Ion-sensitive, field-effect transistors (ISFET) have been useful biosensors in many applications. However, the signal-to-noise ratio of the ISFET is limited by its intrinsic, low-frequency noise. This paper presents an ISFET capable of utilizing lateral-bipolar conduction to reduce low-frequency noise. With a particular layout design, the conduction efficiency is further enhanced. Moreover, the ISFET is compatible with the standard CMOS technology. All materials above the gate-oxide are removed by simple, die-level post-CMOS process, allowing ions to modulate the lateral-bipolar current directly. By varying the gate-to-bulk voltage, the operation mode of the ISFET is controlled effectively, so is the noise performance measured and compared. Finally, the biasing conditions preferable for different low-noise applications are identified. Under the identified biasing condition, the signal-to-noise ratio of the ISFET as a pH sensor is proved to be improved by more than five times. Full article

(This article belongs to the Special Issue ISFET Sensors)

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Graphical abstract

453 KiB

Open AccessReview

Turbidimeter Design and Analysis: A Review on Optical Fiber Sensors for the Measurement of Water Turbidity

by Ahmad Fairuz Bin Omar and Mohd Zubir Bin MatJafri

Sensors 2009, 9(10), 8311-8335; https://doi.org/10.3390/s91008311 - 20 Oct 2009

Cited by 144 | Viewed by 31093

Abstract

Turbidimeters operate based on the optical phenomena that occur when incident light through water body is scattered by the existence of foreign particles which are suspended within it. This review paper elaborates on the standards and factors that may influence the measurement of [...] Read more.

Turbidimeters operate based on the optical phenomena that occur when incident light through water body is scattered by the existence of foreign particles which are suspended within it. This review paper elaborates on the standards and factors that may influence the measurement of turbidity. The discussion also focuses on the optical fiber sensor technologies that have been applied within the lab and field environment and have been implemented in the measurement of water turbidity and concentration of particles. This paper also discusses and compares results from three different turbidimeter designs that use various optical components. Mohd Zubir and Bashah and Daraigan have introduced a design which has simple configurations. Omar and MatJafri, on the other hand, have established a new turbidimeter design that makes use of optical fiber cable as the light transferring medium. The application of fiber optic cable to the turbidimeter will present a flexible measurement technique, allowing measurements to be made online. Scattered light measurement through optical fiber cable requires a highly sensitive detector to interpret the scattered light signal. This has made the optical fiber system have higher sensitivity in measuring turbidity compared to the other two simple turbidimeters presented in this paper. Fiber optic sensors provide the potential for increased sensitivity over large concentration ranges. However, many challenges must be examined to develop sensors that can collect reliable turbidity measurements in situ. Full article

(This article belongs to the Section Chemical Sensors)

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1292 KiB

Open AccessArticle

Cross-Layer Active Predictive Congestion Control Protocol for Wireless Sensor Networks

by Jiangwen Wan, Xiaofeng Xu, Renjian Feng and Yinfeng Wu

Sensors 2009, 9(10), 8278-8310; https://doi.org/10.3390/s91008278 - 20 Oct 2009

Cited by 18 | Viewed by 12040

Abstract

In wireless sensor networks (WSNs), there are numerous factors that may cause network congestion problems, such as the many-to-one communication modes, mutual interference of wireless links, dynamic changes of network topology and the memory-restrained characteristics of nodes. All these factors result in a [...] Read more.

In wireless sensor networks (WSNs), there are numerous factors that may cause network congestion problems, such as the many-to-one communication modes, mutual interference of wireless links, dynamic changes of network topology and the memory-restrained characteristics of nodes. All these factors result in a network being more vulnerable to congestion. In this paper, a cross-layer active predictive congestion control scheme (CL-APCC) for improving the performance of networks is proposed. Queuing theory is applied in the CL-APCC to analyze data flows of a single-node according to its memory status, combined with the analysis of the average occupied memory size of local networks. It also analyzes the current data change trends of local networks to forecast and actively adjust the sending rate of the node in the next period. In order to ensure the fairness and timeliness of the network, the IEEE 802.11 protocol is revised based on waiting time, the number of the node‟s neighbors and the original priority of data packets, which dynamically adjusts the sending priority of the node. The performance of CL-APCC, which is evaluated by extensive simulation experiments. is more efficient in solving the congestion in WSNs. Furthermore, it is clear that the proposed scheme has an outstanding advantage in terms of improving the fairness and lifetime of networks. Full article

(This article belongs to the Section Chemical Sensors)

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198 KiB

Open AccessCommunication

Fluorescence Enhancement of Fluorescein Isothiocyanate-Labeled Protein A Caused by Affinity Binding with Immunoglobulin G in Bovine Plasma

by Takehito Ogawa, Satoka Aoyagi, Takehiro Miyasaka and Kiyotaka Sakai

Sensors 2009, 9(10), 8271-8277; https://doi.org/10.3390/s91008271 - 20 Oct 2009

Cited by 16 | Viewed by 13084

Abstract

Fluorescence enhancement of fluorescein isothiocyanate-labeled protein A (FITC-protein A) caused by the binding with immunoglobulin G (IgG) in bovine plasma was studied. FITC-protein A was immobilized onto a glass surface by covalent bonds. An increase in fluorescence intensity was dependent on IgG concentration [...] Read more.

Fluorescence enhancement of fluorescein isothiocyanate-labeled protein A (FITC-protein A) caused by the binding with immunoglobulin G (IgG) in bovine plasma was studied. FITC-protein A was immobilized onto a glass surface by covalent bonds. An increase in fluorescence intensity was dependent on IgG concentration ranging from 20 to 78 μg/mL in both phosphate buffer saline and bovine plasma. This method requires no separation procedure, and the reaction time is less than 15 min. A fluorescence enhancement assay by the affinity binding of fluorescence-labeled reagent is thus available for the rapid determination of biomolecules in plasma. Full article

(This article belongs to the Section Biosensors)

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256 KiB

Open AccessArticle

Major Improvements of Quartz Crystal Pulling Sensitivity and Linearity Using Series Reactance

by Vojko Matko and Riko Šafarič

Sensors 2009, 9(10), 8263-8270; https://doi.org/10.3390/s91008263 - 19 Oct 2009

Cited by 22 | Viewed by 10695

Abstract

This paper presents a new method of substantially improving frequency pullability and linearity using reactance in series with an AT fundamental crystal operated with a series load capacitance in the range of 3 to 50 pF and frequencies in the range of 3.5 [...] Read more.

This paper presents a new method of substantially improving frequency pullability and linearity using reactance in series with an AT fundamental crystal operated with a series load capacitance in the range of 3 to 50 pF and frequencies in the range of 3.5 to 21 MHz. The research describes high quartz pullability and linearity by varying the load capacitance. The paper also gives impedance circuits for crystal unit (3.5 MHz) together with load capacitance and compensation reactance. The experimental results show that the new approach using compensation method of quartz crystal connected in series reactance increases the frequency pulling range by ×25 to ×100 depending on the type of oscillator and compensation factor ˝k˝ in the temperature range of 10 to 40 °C. Full article

(This article belongs to the Special Issue Sensor Configuration and Smart Sensors)

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1532 KiB

Open AccessReview

Breath Analysis Using Laser Spectroscopic Techniques: Breath Biomarkers, Spectral Fingerprints, and Detection Limits

by Chuji Wang and Peeyush Sahay

Sensors 2009, 9(10), 8230-8262; https://doi.org/10.3390/s91008230 - 19 Oct 2009

Cited by 526 | Viewed by 33998

Abstract

Breath analysis, a promising new field of medicine and medical instrumentation, potentially offers noninvasive, real-time, and point-of-care (POC) disease diagnostics and metabolic status monitoring. Numerous breath biomarkers have been detected and quantified so far by using the GC-MS technique. Recent advances in laser [...] Read more.

Breath analysis, a promising new field of medicine and medical instrumentation, potentially offers noninvasive, real-time, and point-of-care (POC) disease diagnostics and metabolic status monitoring. Numerous breath biomarkers have been detected and quantified so far by using the GC-MS technique. Recent advances in laser spectroscopic techniques and laser sources have driven breath analysis to new heights, moving from laboratory research to commercial reality. Laser spectroscopic detection techniques not only have high-sensitivity and high-selectivity, as equivalently offered by the MS-based techniques, but also have the advantageous features of near real-time response, low instrument costs, and POC function. Of the approximately 35 established breath biomarkers, such as acetone, ammonia, carbon dioxide, ethane, methane, and nitric oxide, 14 species in exhaled human breath have been analyzed by high-sensitivity laser spectroscopic techniques, namely, tunable diode laser absorption spectroscopy (TDLAS), cavity ringdown spectroscopy (CRDS), integrated cavity output spectroscopy (ICOS), cavity enhanced absorption spectroscopy (CEAS), cavity leak-out spectroscopy (CALOS), photoacoustic spectroscopy (PAS), quartz-enhanced photoacoustic spectroscopy (QEPAS), and optical frequency comb cavity-enhanced absorption spectroscopy (OFC-CEAS). Spectral fingerprints of the measured biomarkers span from the UV to the mid-IR spectral regions and the detection limits achieved by the laser techniques range from parts per million to parts per billion levels. Sensors using the laser spectroscopic techniques for a few breath biomarkers, e.g., carbon dioxide, nitric oxide, etc. are commercially available. This review presents an update on the latest developments in laser-based breath analysis. Full article

(This article belongs to the Special Issue Gas Sensors 2009)

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Illustration of the CRDS concept. The effective absorption path-length is readily increased more than 10,000-fold in CRDS. With and without absorption the decay time constants (ringdown times) are different; a ringdown decay example is shown in the right. Full article ">
The combined time-domain and broadband ICOS spectra of the weak oxygen b-x (1,0) band is clearly seen. The broadband-ICOS spectrum can be recovered by doing a linear integration along a line at any constant height (the time axis in the Spectral Photography image) (reproduced with permission from the Optical Society of America [<a href="#b37-sensors-09-08230" class="html-bibr">37</a>]). Full article ">
Schematic of photoacoustic spectroscopy. Full article ">
Schematic of the cavity-enhanced direct-frequency-comb spectrometer, along with the gas handling system for breath analysis (reproduced with permission from the Optical Society of America [<a href="#b50-sensors-09-08230" class="html-bibr">50</a>]). Full article ">
A prototype acetone breath analyzer using pulsed-CRDS at 266 nm. Left: The instrumental package; right: Detailed pictorial view of the optical cavity configuration. Full article ">
Typical measurement of single-breath concentrations of C2H6, CO2, and O2. Each single expiration is analyzed separately. Only 160 s are displayed in the 360–520 s time windown. The complete measurement took 42 min. (Reproduced with permission from Spinger Link [<a href="#b45-sensors-09-08230" class="html-bibr">45</a>]). Full article ">

507 KiB

Open AccessArticle

Sensor Calibration Based on Incoherent Optical Fiber Bundles (IOFB) Used For Remote Image Transmission

by José L. Lázaro, Pedro R. Fernández, Alfredo Gardel, Angel E. Cano and Carlos A. Luna

Sensors 2009, 9(10), 8215-8229; https://doi.org/10.3390/s91008215 - 19 Oct 2009

Cited by 7 | Viewed by 15838

Abstract

Image transmission using incoherent optical fiber bundles (IOFB) requires prior calibration to obtain the spatial in-out fiber correspondence in order to reconstruct the image captured by the pseudo-sensor. This information is recorded in a Look-Up Table (LUT), used later for reordering the fiber [...] Read more.

Image transmission using incoherent optical fiber bundles (IOFB) requires prior calibration to obtain the spatial in-out fiber correspondence in order to reconstruct the image captured by the pseudo-sensor. This information is recorded in a Look-Up Table (LUT), used later for reordering the fiber positions and reconstructing the original image. This paper presents a method based on line-scan to obtain the in-out correspondence. The results demonstrate that this technique yields a remarkable reduction in processing time and increased image quality by introducing a fiber detection algorithm, an intensity compensation process and finally, a single interpolation algorithm. Full article

(This article belongs to the Special Issue Image Sensors 2009)

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1408 KiB

Open AccessArticle

A Distributed Sensor Network for the Control of a Bioclimatic House in Spain

by Álvaro Gutiérrez, Javier Jiménez-Leube and Luis Magdalena

Sensors 2009, 9(10), 8197-8214; https://doi.org/10.3390/s91008197 - 19 Oct 2009

Cited by 8 | Viewed by 13898

Abstract

The XXI century home should be a digital habitat, a connected residence, but at the same time it should be involved in sustainability and the environment. The location of new technologies at home, and its acceptance by the user, requires, among other actions, [...] Read more.

The XXI century home should be a digital habitat, a connected residence, but at the same time it should be involved in sustainability and the environment. The location of new technologies at home, and its acceptance by the user, requires, among other actions, a significant diffusion and activity to be undertaken. This work proposes the development of a Smart House network designed for its integration into a sustainable and bioclimatic solar house. The paper focuses on a specific aspect of the house design, the control system bus, developed for the management of the different parameters, variables, sensors and actuators which coexist at home. Finally, the system has been installed in a laboratory bioclimatic house. Environmental variable experiments based on the control of passive elements, such as phase shift gels, are presented. Experimental results show that the system is able to benefit from the bioclimatic elements in the house by taking into account the user preferences. Full article

(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Spain)

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Graphical abstract

832 KiB

Open AccessReview

Semiconducting Metal Oxide Based Sensors for Selective Gas Pollutant Detection

by Sofian M. Kanan, Oussama M. El-Kadri, Imad A. Abu-Yousef and Marsha C. Kanan

Sensors 2009, 9(10), 8158-8196; https://doi.org/10.3390/s91008158 - 16 Oct 2009

Cited by 373 | Viewed by 29769

Abstract

A review of some papers published in the last fifty years that focus on the semiconducting metal oxide (SMO) based sensors for the selective and sensitive detection of various environmental pollutants is presented. Full article

(This article belongs to the Special Issue Metal-Oxide Based Nanosensors)

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1424 KiB

Open AccessArticle

Biomimetic Yeast Cell Typing—Application of QCMs

by Karin Seidler, Miroslava Polreichová, Peter A. Lieberzeit and Franz L. Dickert

Sensors 2009, 9(10), 8146-8157; https://doi.org/10.3390/s91008146 - 16 Oct 2009

Cited by 23 | Viewed by 13130

Abstract

Artificial antibodies represent a key factor in the generation of sensing systems for the selective detection of bioanalytes of variable sizes. With biomimetic surfaces, the important model organism Saccharomyces cerevisiae and several of its growth stages may be detected. Quartz crystal microbalances (QCM) [...] Read more.

Artificial antibodies represent a key factor in the generation of sensing systems for the selective detection of bioanalytes of variable sizes. With biomimetic surfaces, the important model organism Saccharomyces cerevisiae and several of its growth stages may be detected. Quartz crystal microbalances (QCM) with 10 MHz fundamental frequency and coated with polymers imprinted with synchronized yeast cells are presented, which are able to detect duplex cells with high selectivity. Furthermore, a multichannel quartz crystal microbalance (MQCM) was designed and optimized for the measurement in liquids. This one-chip system based on four-electrode geometry allows the simultaneous detection of four analytes and, thus, provides a monitoring system for biotechnology and process control. For further standardization of the method, synthetic stamps containing plastic yeast cells in different growth stages were produced and utilized for imprinting. Mass-sensitive measurements with such MIPs resulted in the same sensor characteristics as obtained for those imprinted with native yeast cells. Full article

(This article belongs to the Section Chemical Sensors)

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437 KiB

Open AccessReview

Magnetic Nanoparticle Sensors

by Isaac Koh and Lee Josephson

Sensors 2009, 9(10), 8130-8145; https://doi.org/10.3390/s91008130 - 16 Oct 2009

Cited by 283 | Viewed by 23406

Abstract

Many types of biosensors employ magnetic nanoparticles (diameter = 5–300 nm) or magnetic particles (diameter = 300–5,000 nm) which have been surface functionalized to recognize specific molecular targets. Here we cover three types of biosensors that employ different biosensing principles, magnetic materials, and [...] Read more.

Many types of biosensors employ magnetic nanoparticles (diameter = 5–300 nm) or magnetic particles (diameter = 300–5,000 nm) which have been surface functionalized to recognize specific molecular targets. Here we cover three types of biosensors that employ different biosensing principles, magnetic materials, and instrumentation. The first type consists of magnetic relaxation switch assay-sensors, which are based on the effects magnetic particles exert on water proton relaxation rates. The second type consists of magnetic particle relaxation sensors, which determine the relaxation of the magnetic moment within the magnetic particle. The third type is magnetoresistive sensors, which detect the presence of magnetic particles on the surface of electronic devices that are sensitive to changes in magnetic fields on their surface. Recent improvements in the design of magnetic nanoparticles (and magnetic particles), together with improvements in instrumentation, suggest that magnetic material-based biosensors may become widely used in the future. Full article

(This article belongs to the Special Issue Nanotechnological Advances in Biosensors)

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Principle of Type I MRSws. Dispersed magnetic nanoparticles (NPs) form an aggregate upon binding with target analytes (triangle). The aggregated form of the NPs dephases the spins of the surrounding protons of water molecules more efficiently than NPs present as the dispersed state. The effect is observed as a decrease in spin-spin relaxation time, T2 (reproduced with permission from reference [<a href="#b52-sensors-09-08130" class="html-bibr">52</a>]). Full article ">
Methods for the improvement in MRSw assay sensitivities. (A) MPs (●) aggregate in a homogeneous magnetic field, whereas NPs (□) do not respond. A T2 increase in time is observed in a 0.47 T field (gray) in an MP solution, but not in an NP solution. The T2 value of the MP solution decreases as the MPs are dispersed with the field turn-off (white). Note that a T2 increase is observed with MP aggregation. (type II MRSw). Since this effect is slowed by the viscosity of the medium, T2-based viscometer can be obtained, see [<a href="#b7-sensors-09-08130" class="html-bibr">7</a>]. (B) Three strategies for enhancing the sensitivities with a type II MRSw assay. (a) A decreased concentration of MPs formed aggregates at a lower concentration of analyte (anti-Tag antibody) than that of NPs. MPs are larger than NPs and used at a lower concentration. (b) Application of a magnetic field (0.47 T) induced aggregation of MPs as in (A) and accelerated the interaction between MPs and analytes. (c) Target valency enhancement by addition of a secondary antibody (sheep anti-mouse). The valency increase of targets from two (anti Tag) to four (anti Tag:anti mouse) enhanced MRSw sensitivities. Figure reproduced with permission from reference [<a href="#b6-sensors-09-08130" class="html-bibr">6</a>]. Full article ">
(A). Schematic representation of a miniaturized chip-based NMR system, diagnostic magnetic resonance (DMR). (B). NMR based CMOS RF biosensor. A complete NMR system was built with a portable platform (reproduced with permission (A) from reference [<a href="#b10-sensors-09-08130" class="html-bibr">10</a>] and (B) from reference [<a href="#b21-sensors-09-08130" class="html-bibr">21</a>]). Full article ">
Principle of a SQUID-based homogeneous detector of bacteria. A. A pulse-form magnetic field orients the magnetic moments of NPs. B. After the field pulse is over, Brownian motion randomizes the magnetic moments of unbound NPs. However, the Brownian rotations of NPs bound to the bacteria are restricted. The bound NPs undergo Néel relaxation for reorientation of the magnetic moments. The SQUID detects the slower Néel relaxation for the bound NPs (reproduced with permission from reference [<a href="#b36-sensors-09-08130" class="html-bibr">36</a>]). Full article ">
A schematic representation of a giant magnetoresistive (GMR) sensor for an ELISA-type protein assay. A. The probe surface was functionalized with a specific antibody, while the control surface was passivated with BSA. B. A sample solution was added for a specific binding of analyte proteins to the probe surface. C. A biotinylated antibody bound to the surface-immobilized analytes. D. Finally streptavidin-coated NPs were added for tagging the probe surface by biotin-streptavidin interaction. GMR signals were detected for sensing the presence of analytes on the surface. Courtesy from [<a href="#b48-sensors-09-08130" class="html-bibr">48</a>]. Full article ">

143 KiB

Open AccessEditorial

Guest Editor’s Concluding Remarks―Advances in Usage of ANN, Discussion of an Unsolved Problem, and Some Differences between Papers Written by Engineers and by Physicians

by Michael W. Retsky

Sensors 2009, 9(10), 8126-8129; https://doi.org/10.3390/s91008126 - 16 Oct 2009

Viewed by 13114

Abstract

I take this opportunity to discuss a few things that I have learned from being Guest Editor of this special issue of Sensors devoted to Neural Networks and Sensors. The advancement in artificial neural network (ANN) technology is very impressive. The wide variety [...] Read more.

I take this opportunity to discuss a few things that I have learned from being Guest Editor of this special issue of Sensors devoted to Neural Networks and Sensors. The advancement in artificial neural network (ANN) technology is very impressive. The wide variety of fields in which this technology applies in the form of practical applications to clearly identifiable real problems demonstrates that ANNs are being routinely used to solve non-trivial problems. I mention that because A. K. Dewdney wrote in 1997 that while ANNs have been used to solve a few toy problems, he was surprised that anyone takes them seriously as general problem-solving tools [1]. The ANN applications reported by Yu Liu et al. [2], Erkan Beşdok [3], Guillermo Zatorre et al. [4], Amir Jabbari et al. [5], Mohamed Lamine Hafiane et al. [6], Kai-Wei Chiang et al. [7], Raúl Vicen-Bueno et al. [8], Juan L. Pedreño-Molina et al. [9], and P. B. Garcia-Allende et al. [10] are far more than toy applications. The lesson to be learned here is that it is a bad idea to publically bet against technological progress in computer applications. [...] Full article

(This article belongs to the Special Issue Neural Networks and Sensors)

161 KiB

Open AccessArticle

Neural Network Emulation of the Integral Equation Model with Multiple Scattering

by Luca Pulvirenti, Francesca Ticconi and Nazzareno Pierdicca

Sensors 2009, 9(10), 8109-8125; https://doi.org/10.3390/s91008109 - 15 Oct 2009

Cited by 3 | Viewed by 11976

Abstract

The Integral Equation Model with multiple scattering (IEMM) represents a well-established method that provides a theoretical framework for the scattering of electromagnetic waves from rough surfaces. A critical aspect is the long computational time required to run such a complex model. To deal [...] Read more.

The Integral Equation Model with multiple scattering (IEMM) represents a well-established method that provides a theoretical framework for the scattering of electromagnetic waves from rough surfaces. A critical aspect is the long computational time required to run such a complex model. To deal with this problem, a neural network technique is proposed in this work. In particular, we have adopted neural networks to reproduce the backscattering coefficients predicted by IEMM at L- and C-bands, thus making reference to presently operative satellite radar sensors, i.e., that aboard ERS-2, ASAR on board ENVISAT (C-band), and PALSAR aboard ALOS (L-band). The neural network-based model has been designed for radar observations of both flat and tilted surfaces, in order to make it applicable for hilly terrains too. The assessment of the proposed approach has been carried out by comparing neural network-derived backscattering coefficients with IEMM-derived ones. Different databases with respect to those employed to train the networks have been used for this purpose. The outcomes seem to prove the feasibility of relying on a neural network approach to efficiently and reliably approximate an electromagnetic model of surface scattering. Full article

(This article belongs to the Special Issue Neural Networks and Sensors)

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The Neural Network architectures. Upper panel: NN topology for the nominal incidence angle (Ni = 3, Nh1 = 15, Nh2 = 10, No = 2); lower panel: NN topology for incidence angle assumed as an additional input parameter (Ni = 4, Nh1 = 30, Nh2 = 25, No = 2). Full article ">
Comparison between IEMM- and NN-derived σ0 (test sets of 500 records). Left panels: vertical polarization; right panels: horizontal polarization. Upper panels: L-band; lower panels: C-band. Dotted lines represent perfect agreement. Full article ">
Comparison between IEMM- and NN-derived σ0 (test sets of 500 records). Left panels: vertical polarization; right panels: horizontal polarization. Upper panels: L-band; lower panels: C-band. Dotted lines represent perfect agreement. Full article ">
Trend of the rmse (error bars) versus k0s. Left panels: vertical polarization; right panels: horizontal polarization. Upper panels: L-band; lower panels: C-band. Full article ">
Same as <a href="#f2-sensors-09-08109" class="html-fig">Figure 2</a>, but for θi assumed as an additional input parameter (test sets of 4,000 records). Full article ">
Same as <a href="#f2-sensors-09-08109" class="html-fig">Figure 2</a>, but for θi assumed as an additional input parameter (test sets of 4,000 records). Full article ">
Same as <a href="#f3-sensors-09-08109" class="html-fig">Figure 3</a>, but for θi assumed as an additional input parameter. Full article ">

350 KiB

Open AccessArticle

Efficient Aggregation of Multiple Classes of Information in Wireless Sensor Networks

by Xiaoling Qiu, Haiping Liu, Deshi Li, Jennifer Yick, Dipak Ghosal and Biswanath Mukherjee

Sensors 2009, 9(10), 8083-8108; https://doi.org/10.3390/s91008083 - 14 Oct 2009

Cited by 11 | Viewed by 16527

Abstract

Congestion in a Wireless Sensor Network (WSN) can lead to buffer overflow, resource waste and delay or loss of critical information from the sensors. In this paper, we propose the Priority-based Coverage-aware Congestion Control (PCC) algorithm which is distributed, priority-distinct, and [...] Read more.

Congestion in a Wireless Sensor Network (WSN) can lead to buffer overflow, resource waste and delay or loss of critical information from the sensors. In this paper, we propose the Priority-based Coverage-aware Congestion Control (PCC) algorithm which is distributed, priority-distinct, and fair. PCC provides higher priority to packets with event information in which the sink is more interested. PCC employs a queue scheduler that can selectively drop any packet in the queue. PCC gives fair chance to all sensors to send packets to the sink, irrespective of their specific locations, and therefore enhances the coverage fidelity of theWSN. Based on a detailed simulation analysis, we show that PCC can efficiently relieve congestion and significantly improve the system performance based on multiple metrics such as event throughput and coverage fidelity. We generalize PCC to address data collection in a WSN in which the sensor nodes have multiple sensing devices and can generate multiple types of information. We propose a Pricing System that can under congestion effectively collect different types of data generated by the sensor nodes according to values that are placed on different information by the sink. Simulation analysis show that our Pricing System can achieve higher event throughput for packets with higher priority and achieve fairness among different categories. Moreover, given a fixed system capacity, our proposed Pricing System can collect more information of the type valued by the sink. Full article

(This article belongs to the Special Issue Wireless Sensor Technologies and Applications)

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Graphical abstract

70 KiB

Open AccessArticle

Identification of Tea Storage Times by Linear Discrimination Analysis and Back-Propagation Neural Network Techniques Based on the Eigenvalues of Principal Components Analysis of E-Nose Sensor Signals

by Huichun Yu, Yongwei Wang and Jun Wang

Sensors 2009, 9(10), 8073-8082; https://doi.org/10.3390/s91008073 - 14 Oct 2009

Cited by 50 | Viewed by 13904

Abstract

An electronic nose (E-nose) was employed to detect the aroma of green tea after different storage times. Longjing green tea dry leaves, beverages and residues were detected with an E-nose, respectively. In order to decrease the data dimensionality and optimize the feature vector, [...] Read more.

An electronic nose (E-nose) was employed to detect the aroma of green tea after different storage times. Longjing green tea dry leaves, beverages and residues were detected with an E-nose, respectively. In order to decrease the data dimensionality and optimize the feature vector, the E-nose sensor response data were analyzed by principal components analysis (PCA) and the five main principal components values were extracted as the input for the discrimination analysis. The storage time (0, 60, 120, 180 and 240 days) was better discriminated by linear discrimination analysis (LDA) and was predicted by the back-propagation neural network (BPNN) method. The results showed that the discrimination and testing results based on the tea leaves were better than those based on tea beverages and tea residues. The mean errors of the tea leaf data were 9, 2.73, 3.93, 6.33 and 6.8 days, respectively. Full article

(This article belongs to the Section Chemical Sensors)

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2061 KiB

Open AccessArticle

A Radio-Aware Routing Algorithm for Reliable Directed Diffusion in Lossy Wireless Sensor Networks

by Yong-Pyo Kim, Euihyun Jung and Yong-Jin Park

Sensors 2009, 9(10), 8047-8072; https://doi.org/10.3390/s91008047 - 13 Oct 2009

Cited by 7 | Viewed by 14388

Abstract

In Wireless Sensor Networks (WSNs), transmission errors occur frequently due to node failure, battery discharge, contention or interference by objects. Although Directed Diffusion has been considered as a prominent data-centric routing algorithm, it has some weaknesses due to unexpected network errors. In order [...] Read more.

In Wireless Sensor Networks (WSNs), transmission errors occur frequently due to node failure, battery discharge, contention or interference by objects. Although Directed Diffusion has been considered as a prominent data-centric routing algorithm, it has some weaknesses due to unexpected network errors. In order to address these problems, we proposed a radio-aware routing algorithm to improve the reliability of Directed Diffusion in lossy WSNs. The proposed algorithm is aware of the network status based on the radio information from MAC and PHY layers using a cross-layer design. The cross-layer design can be used to get detailed information about current status of wireless network such as a link quality or transmission errors of communication links. The radio information indicating variant network conditions and link quality was used to determine an alternative route that provides reliable data transmission under lossy WSNs. According to the simulation result, the radio-aware reliable routing algorithm showed better performance in both grid and random topologies with various error rates. The proposed solution suggested the possibility of providing a reliable transmission method for QoS requests in lossy WSNs based on the radio-awareness. The energy and mobility issues will be addressed in the future work. Full article

(This article belongs to the Special Issue Sensor Algorithms)

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746 KiB

Open AccessArticle

Fabrication of Poly(p-Phenylene)/Zeolite Composites and Their Responses Towards Ammonia

by Pimchanok Phumman, Sumonman Niamlang and Anuvat Sirivat

Sensors 2009, 9(10), 8031-8046; https://doi.org/10.3390/s91008031 - 13 Oct 2009

Cited by 22 | Viewed by 12912

Abstract

Poly(p-phenylene) (PPP) was chemically synthesized via oxidative polymerization using benzene and doped with FeCl₃. The electrical conductivity response of the doped PPP (dPPP) towards CO, H₂ and NH₃ is investigated. dPPP shows no electrical conductivity response towards [...] Read more.

Poly(p-phenylene) (PPP) was chemically synthesized via oxidative polymerization using benzene and doped with FeCl₃. The electrical conductivity response of the doped PPP (dPPP) towards CO, H₂ and NH₃ is investigated. dPPP shows no electrical conductivity response towards the first two gases (CO and H₂), but it shows a definite negative response towards NH₃. The electrical conductivity sensitivity of dPPP increases linearly with increasing NH₃ concentration. To improve the sensitivity of the sensor towards NH₃, ZSM-5 zeolite is added into the conductive polymer matrix. The electrical sensitivity of the sensor increases with increasing zeolite content up to 30%. The effect of the type of cation in the zeolite pores is investigated: namely, Na⁺, K⁺, NH₄⁺and H⁺. The electrical conductivity sensitivity of the composites with different cations in the zeolite can be arranged in this order: K⁺ < no zeolite < Na⁺ < NH₄⁺< H⁺. The variation in electrical sensitivity with cation type can be described in terms of the acid-base interaction, the zeolite pore size and surface area. The PPP/Zeolite composite with H⁺ possesses the highest electrical sensitivity of −0.36 since H⁺ has the highest acidity, the highest pore volume and surface area, which combine to induce a more favorable NH₃ adsorption and interaction with the conductive polymer. Full article

(This article belongs to the Section Chemical Sensors)

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661 KiB

Open AccessArticle

Collaborative Distributed Scheduling Approaches for Wireless Sensor Network

by Jianjun Niu and Zhidong Deng

Sensors 2009, 9(10), 8007-8030; https://doi.org/10.3390/s91008007 - 13 Oct 2009

Cited by 4 | Viewed by 10266

Abstract

Energy constraints restrict the lifetime of wireless sensor networks (WSNs) with battery-powered nodes, which poses great challenges for their large scale application. In this paper, we propose a family of collaborative distributed scheduling approaches (CDSAs) based on the Markov process to reduce the [...] Read more.

Energy constraints restrict the lifetime of wireless sensor networks (WSNs) with battery-powered nodes, which poses great challenges for their large scale application. In this paper, we propose a family of collaborative distributed scheduling approaches (CDSAs) based on the Markov process to reduce the energy consumption of a WSN. The family of CDSAs comprises of two approaches: a one-step collaborative distributed approach and a two-step collaborative distributed approach. The approaches enable nodes to learn the behavior information of its environment collaboratively and integrate sleep scheduling with transmission scheduling to reduce the energy consumption. We analyze the adaptability and practicality features of the CDSAs. The simulation results show that the two proposed approaches can effectively reduce nodes’ energy consumption. Some other characteristics of the CDSAs like buffer occupation and packet delay are also analyzed in this paper. We evaluate CDSAs extensively on a 15-node WSN testbed. The test results show that the CDSAs conserve the energy effectively and are feasible for real WSNs. Full article

(This article belongs to the Special Issue Sensor Algorithms)

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971 KiB

Open AccessArticle

A Coupled Field Multiphysics Modeling Approach to Investigate RF MEMS Switch Failure Modes under Various Operational Conditions

by Khaled Sadek, Jonathan Lueke and Walied Moussa

Sensors 2009, 9(10), 7988-8006; https://doi.org/10.3390/s91007988 - 12 Oct 2009

Cited by 11 | Viewed by 13064

Abstract

In this paper, the reliability of capacitive shunt RF MEMS switches have been investigated using three dimensional (3D) coupled multiphysics finite element (FE) analysis. The coupled field analysis involved three consecutive multiphysics interactions. The first interaction is characterized as a two-way sequential electromagnetic [...] Read more.

In this paper, the reliability of capacitive shunt RF MEMS switches have been investigated using three dimensional (3D) coupled multiphysics finite element (FE) analysis. The coupled field analysis involved three consecutive multiphysics interactions. The first interaction is characterized as a two-way sequential electromagnetic (EM)-thermal field coupling. The second interaction represented a one-way sequential thermal-structural field coupling. The third interaction portrayed a two-way sequential structural-electrostatic field coupling. An automated substructuring algorithm was utilized to reduce the computational cost of the complicated coupled multiphysics FE analysis. The results of the substructured FE model with coupled field analysis is shown to be in good agreement with the outcome of previously published experimental and numerical studies. The current numerical results indicate that the pull-in voltage and the buckling temperature of the RF switch are functions of the microfabrication residual stress state, the switch operational frequency and the surrounding packaging temperature. Furthermore, the current results point out that by introducing proper mechanical approaches such as corrugated switches and through-holes in the switch membrane, it is possible to achieve reliable pull-in voltages, at various operating temperatures. The performed analysis also shows that by controlling the mean and gradient residual stresses, generated during microfabrication, in conjunction with the proposed mechanical approaches, the power handling capability of RF MEMS switches can be increased, at a wide range of operational frequencies. These design features of RF MEMS switches are of particular importance in applications where a high RF power (frequencies above 10 GHz) and large temperature variations are expected, such as in satellites and airplane condition monitoring. Full article

(This article belongs to the Special Issue Modeling, Testing and Reliability Issues in MEMS Engineering - 2009)

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1492 KiB

Open AccessArticle

Micro Sensor Node for Air Pollutant Monitoring: Hardware and Software Issues

by Sukwon Choi, Nakyoung Kim, Hojung Cha and Rhan Ha

Sensors 2009, 9(10), 7970-7987; https://doi.org/10.3390/s91007970 - 12 Oct 2009

Cited by 91 | Viewed by 17898

Abstract

Wireless sensor networks equipped with various gas sensors have been actively used for air quality monitoring. Previous studies have typically explored system issues that include middleware or networking performance, but most research has barely considered the details of the hardware and software of [...] Read more.

Wireless sensor networks equipped with various gas sensors have been actively used for air quality monitoring. Previous studies have typically explored system issues that include middleware or networking performance, but most research has barely considered the details of the hardware and software of the sensor node itself. In this paper, we focus on the design and implementation of a sensor board for air pollutant monitoring applications. Several hardware and software issues are discussed to explore the possibilities of a practical WSN-based air pollution monitoring system. Through extensive experiments and evaluation, we have determined the various characteristics of the gas sensors and their practical implications for air pollutant monitoring systems. Full article

(This article belongs to the Special Issue Modeling, Testing and Reliability Issues in MEMS Engineering - 2009)

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522 KiB

Open AccessArticle

A Label-Free Electronic Biosensor for Detection of Bone Turnover Markers

by Yeo-Heung Yun, Amit Bhattacharya, Nelson B. Watts and Mark J. Schulz

Sensors 2009, 9(10), 7957-7969; https://doi.org/10.3390/s91007957 - 12 Oct 2009

Cited by 39 | Viewed by 15243

Abstract

This paper describes the development of a biosensor based on label-free immunosensing for the detection of the C-terminal telopeptide bone turnover marker from type-1 collagen. A self-assembled monolayer (SAM) of dithiodipropionic acid was deposited on a gold electrode. Then streptavidin and biotinylated anti-human [...] Read more.

This paper describes the development of a biosensor based on label-free immunosensing for the detection of the C-terminal telopeptide bone turnover marker from type-1 collagen. A self-assembled monolayer (SAM) of dithiodipropionic acid was deposited on a gold electrode. Then streptavidin and biotinylated anti-human C-terminal telopeptide antibody were successively conjugated on the self-assembled monolayer. Electrochemical impedance measurements were made to characterize each step of the SAM/streptavidin/biotinylated antibody binding. Subsequently, electrochemical impedance was measured with different concentrations of C-teminal telopeptide. A detection limit of 50 ng/mL and a dynamic range up to 3 μg/mL were achieved. To our knowledge, this is the first attempt to develop a label-free immunosensor based on electrochemical impedance with DC bias for detection of bone-related degradation and rebuilding products. The electronic biosensor might eventually be used for quantitative point-of-care screening of bone health. It is hoped that analysis of bone turnover markers can indicate the beginning of bone diseases such as osteoarthritis and osteoporosis so that treatment might start early when it is most effective. Full article

(This article belongs to the Section Biosensors)

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1559 KiB

Open AccessArticle

Vehicle Signal Analysis Using Artificial Neural Networks for a Bridge Weigh-in-Motion System

by Sungkon Kim, Jungwhee Lee, Min-Seok Park and Byung-Wan Jo

Sensors 2009, 9(10), 7943-7956; https://doi.org/10.3390/s91007943 - 12 Oct 2009

Cited by 48 | Viewed by 13864

Abstract

This paper describes the procedures for development of signal analysis algorithms using artificial neural networks for Bridge Weigh-in-Motion (B-WIM) systems. Through the analysis procedure, the extraction of information concerning heavy traffic vehicles such as weight, speed, and number of axles from the time [...] Read more.

This paper describes the procedures for development of signal analysis algorithms using artificial neural networks for Bridge Weigh-in-Motion (B-WIM) systems. Through the analysis procedure, the extraction of information concerning heavy traffic vehicles such as weight, speed, and number of axles from the time domain strain data of the B-WIM system was attempted. As one of the several possible pattern recognition techniques, an Artificial Neural Network (ANN) was employed since it could effectively include dynamic effects and bridge-vehicle interactions. A number of vehicle traveling experiments with sufficient load cases were executed on two different types of bridges, a simply supported pre-stressed concrete girder bridge and a cable-stayed bridge. Different types of WIM systems such as high-speed WIM or low-speed WIM were also utilized during the experiments for cross-checking and to validate the performance of the developed algorithms. Full article

(This article belongs to the Special Issue Neural Networks and Sensors)

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1014 KiB

Open AccessReview

Magnetic Field Sensors Based on Giant Magnetoresistance (GMR) Technology: Applications in Electrical Current Sensing

by Càndid Reig, María-Dolores Cubells-Beltrán and Diego Ramírez Muñoz

Sensors 2009, 9(10), 7919-7942; https://doi.org/10.3390/s91007919 - 12 Oct 2009

Cited by 228 | Viewed by 28512

Abstract

The 2007 Nobel Prize in Physics can be understood as a global recognition to the rapid development of the Giant Magnetoresistance (GMR), from both the physics and engineering points of view. Behind the utilization of GMR structures as read heads for massive storage [...] Read more.

The 2007 Nobel Prize in Physics can be understood as a global recognition to the rapid development of the Giant Magnetoresistance (GMR), from both the physics and engineering points of view. Behind the utilization of GMR structures as read heads for massive storage magnetic hard disks, important applications as solid state magnetic sensors have emerged. Low cost, compatibility with standard CMOS technologies and high sensitivity are common advantages of these sensors. This way, they have been successfully applied in a lot different environments. In this work, we are trying to collect the Spanish contributions to the progress of the research related to the GMR based sensors covering, among other subjects, the applications, the sensor design, the modelling and the electronic interfaces, focusing on electrical current sensing applications. Full article

(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Spain)

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355 KiB

Open AccessArticle

Determination of Diclofenac on a Dysprosium Nanowire- Modified Carbon Paste Electrode Accomplished in a Flow Injection System by Advanced Filtering

by Parandis Daneshgar, Parviz Norouzi, Mohammad Reza Ganjali, Rasoul Dinarvand and Ali Akbar Moosavi-Movahedi

Sensors 2009, 9(10), 7903-7918; https://doi.org/10.3390/s91007903 - 30 Sep 2009

Cited by 45 | Viewed by 13687

Abstract

A new detection technique called Fast Fourier Transform Square-Wave Voltammetry (FFT SWV) is based on measurements of electrode admittance as a function of potential. The response of the detector (microelectrode), which is generated by a redox processes, is fast, which makes the method [...] Read more.

A new detection technique called Fast Fourier Transform Square-Wave Voltammetry (FFT SWV) is based on measurements of electrode admittance as a function of potential. The response of the detector (microelectrode), which is generated by a redox processes, is fast, which makes the method suitable for most applications involving flowing electrolytes. The carbon paste electrode was modified by nanostructures to improve sensitivity. Synthesized dysprosium nanowires provide a more effective nanotube-like surface [1-4] so they are good candidates for use as a modifier for electrochemical reactions. The redox properties of diclofenac were used for its determination in human serum and urine samples. The support electrolyte that provided a more defined and intense peak current for diclofenac determination was a 0.05 mol L⁻¹ acetate buffer pH = 4.0. The drug presented an irreversible oxidation peak at 850 mV vs. Ag/AgCl on a modified nanowire carbon paste electrode which produced high current and reduced the oxidation potential by about 100 mV. Furthermore, the signal-to-noise ratio was significantly increased by application of a discrete Fast Fourier Transform (FFT) method, background subtraction and two-dimensional integration of the electrode response over a selected potential range and time window. To obtain the much sensivity the effective parameters such as frequency, amplitude and pH was optimized. As a result, C_DL of 2.0 × 10⁻⁹ M and an LOQ of 5.0 × 10⁻⁹M were found for the determination for diclofenac. A good recovery was obtained for assay spiked urine samples and a good quantification of diclofenac was achieved in a commercial formulation. Full article

(This article belongs to the Section Chemical Sensors)

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1455 KiB

Open AccessArticle

Synthesis Methods, Microscopy Characterization and Device Integration of Nanoscale Metal Oxide Semiconductors for Gas Sensing

by Randy L. Vander Wal, Gordon M. Berger, Michael J. Kulis, Gary W. Hunter, Jennifer C. Xu and Laura Evans

Sensors 2009, 9(10), 7866-7902; https://doi.org/10.3390/s91007866 - 30 Sep 2009

Cited by 26 | Viewed by 15331

Abstract

A comparison is made between SnO₂, ZnO, and TiO₂single-crystal nanowires and SnO₂ polycrystalline nanofibers for gas sensing. Both nanostructures possess a one-dimensional morphology. Different synthesis methods are used to produce these materials: thermal evaporation-condensation (TEC), controlled oxidation, and [...] Read more.

A comparison is made between SnO₂, ZnO, and TiO₂single-crystal nanowires and SnO₂ polycrystalline nanofibers for gas sensing. Both nanostructures possess a one-dimensional morphology. Different synthesis methods are used to produce these materials: thermal evaporation-condensation (TEC), controlled oxidation, and electrospinning. Advantages and limitations of each technique are listed. Practical issues associated with harvesting, purification, and integration of these materials into sensing devices are detailed. For comparison to the nascent form, these sensing materials are surface coated with Pd and Pt nanoparticles. Gas sensing tests, with respect to H₂, are conducted at ambient and elevated temperatures. Comparative normalized responses and time constants for the catalyst and noncatalyst systems provide a basis for identification of the superior metal-oxide nanostructure and catalyst combination. With temperature-dependent data, Arrhenius analyses are made to determine activation energies for the catalyst-assisted systems. Full article

(This article belongs to the Special Issue Gas Sensors 2009)

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2925 KiB

Open AccessArticle

Integration of an On-Axis General Sun-Tracking Formula in the Algorithm of an Open-Loop Sun-Tracking System

by Kok-Keong Chong, Chee-Woon Wong, Fei-Lu Siaw, Tiong-Keat Yew, See-Seng Ng, Meng-Suan Liang, Yun-Seng Lim and Sing-Liong Lau

Sensors 2009, 9(10), 7849-7865; https://doi.org/10.3390/s91007849 - 30 Sep 2009

Cited by 57 | Viewed by 19387

Abstract

A novel on-axis general sun-tracking formula has been integrated in the algorithm of an open-loop sun-tracking system in order to track the sun accurately and cost effectively. Sun-tracking errors due to installation defects of the 25 m² prototype solar concentrator have been [...] Read more.

A novel on-axis general sun-tracking formula has been integrated in the algorithm of an open-loop sun-tracking system in order to track the sun accurately and cost effectively. Sun-tracking errors due to installation defects of the 25 m² prototype solar concentrator have been analyzed from recorded solar images with the use of a CCD camera. With the recorded data, misaligned angles from ideal azimuth-elevation axes have been determined and corrected by a straightforward changing of the parameters’ values in the general formula of the tracking algorithm to improve the tracking accuracy to 2.99 mrad, which falls below the encoder resolution limit of 4.13 mrad. Full article

(This article belongs to the Section Chemical Sensors)

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Graphical abstract

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Full article ">
The flow chart of the computational program to determine the three unknown orientation angles that cannot be precisely measured by tools in practice, i.e., φ, λ and ζ. Full article ">
A prototype of on-axis solar concentrator that has been constructed at Universiti Tunku Abdul Rahman (UTAR). Full article ">
A Windows-based control program that has been integrated with the on-axis general formula. Full article ">
(a). Block diagram to show the complete open-loop feedback system of the prototype solar concentrator. (b). Schematic diagram to show the detail of the open-loop sun-tracking system of the prototype solar concentrator where AA' is azimuth-axis and BB' is elevation-axis. Full article ">
The recorded solar images on the target of prototype solar concentrator using a CCD camera from 10:07 am. to 4:25 pm. on 13 January 2009 with φ࿠= λ࿠= ζ࿠= 0°. Full article ">
The plot of pointing error (mrad) versus local time (hours) for the parameters, i.e.,࿠φ࿠= λ࿠= ζ࿠= 0°, on 13 January 2009. Full article ">
The plot of pointing error (mrad) versus local time (hours) for the parameters, i.e.,࿠φ࿠= −0.1°; λ࿠= 0°; and ζ࿠= −0.5°, on 16 January 2009. Full article ">
The recorded solar images on the target of prototype solar concentrator using a CCD camera from 10:25 am. to 4:54 pm. on 16 January 2009 with φ࿠= −0.1°; λ࿠= 0°; and ζ࿠= −0.5°. Full article ">

624 KiB

Open AccessArticle

Optimization of TiO₂ and PMAPTAC Concentrations of a Chemical Humidity Sensing Mechanism

by Souhil Kouda, Zohir Dibi, Abdelghani Dendouga, Fayçal Meddour and Samir Barra

Sensors 2009, 9(10), 7837-7848; https://doi.org/10.3390/s91007837 - 30 Sep 2009

Cited by 2 | Viewed by 10460

Abstract

This work aims to achieve an optimization of the TiO₂ and PMAPTAC concentrations in a chemical resistive-type humidity sensing mechanism (RHSM). Our idea is based primarily on the modeling of the sensing mechanism. This model takes into account the parameters of non-linearity, [...] Read more.

This work aims to achieve an optimization of the TiO₂ and PMAPTAC concentrations in a chemical resistive-type humidity sensing mechanism (RHSM). Our idea is based primarily on the modeling of the sensing mechanism. This model takes into account the parameters of non-linearity, hysteresis, temperature, frequency, substrate type. Furthermore, we investigated the TiO₂ and PMAPTAC effects concentrations on the humidity sensing properties in our model. Secondly, we used the Matlab environment to create a database for an ideal model for the sensing mechanism, where the response of this ideal model is linear for any value of the above parameters. We have done the training to create an analytical model for the sensing mechanism (SM) and the ideal model (IM). After that, the SM and IM models are established on PSPICE simulator, where the output of the first is identical to the output of the RHSM used and the output of the last is the ideal response. Finally a “DIF bloc” was realized to make the difference between the SM output and the IM output, where this difference represents the linearity error, we take the minimum error, to identify the optimal TiO₂ and PMAPTAC concentrations. However, a compromise between concentrations, humidity and temperature must be performed. The simulation results show that in low humidity and at temperature more than 25 °C, sample 1 is the best (in alumina substrate). However, the sample 9 represents the best sensor (in PET substrate) predominately for the lowest humidity and temperature. Full article

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827 KiB

Open AccessArticle

Investigation of SOI Raman Lasers for Mid-Infrared Gas Sensing

by Vittorio M. N. Passaro and Francesco De Leonardis

Sensors 2009, 9(10), 7814-7836; https://doi.org/10.3390/s91007814 - 30 Sep 2009

Cited by 19 | Viewed by 13695

Abstract

In this paper, the investigation and detailed modeling of a cascaded Raman laser, operating in the midwave infrared region, is described. The device is based on silicon-on-insulator optical waveguides and a coupled resonant microcavity. Theoretical results are compared with recent experiments, demonstrating a [...] Read more.

In this paper, the investigation and detailed modeling of a cascaded Raman laser, operating in the midwave infrared region, is described. The device is based on silicon-on-insulator optical waveguides and a coupled resonant microcavity. Theoretical results are compared with recent experiments, demonstrating a very good agreement. Design criteria are derived for cascaded Raman lasers working as continuous wave light sources to simultaneously sense two types of gases, namely C₂H₆ and CO₂, at a moderate power level of 130 mW. Full article

(This article belongs to the Special Issue Gas Sensors 2009)

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Sensors, Volume 9, Issue 10 (October 2009) – 41 articles , Pages 7580-8381

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